[Webby]

Right mem speed, depending on what options are available to you in the BIOS will determine how fast the memory runs after the CPU is overclocked basically memory speed is determined by the front side bus (FSB) for the Q9550 the FSB is 1333MHz now this figure has been Quad pumped so the actual frequency is 333MHz when you overclock the processor this is the number you increase. Memory speed is related to the FSB by a 2x multiplier (DDR = double data rate) so if the FSB is 333MHz and you are using a 1:1 divider (more on dividers in a minute) then your memory will be running at 667Mhz.

So dividers they are settings which tell your memory how many times the FSB it should run at so 1:1 means the same speed as the FSB then multiplied by 2 because its DDR, depending on your motherboard a number of dividers will be available to allow faster memory to run at its rated speed.

So back to overclocking so if you have DDR2-800 and a 1:1 divider then you can run the FSB at 400MHz before the memory is overcocked. This would translate to a 20% overclock for the Q9550 and a CPU clock speed of 3.4GHz (assuming the CPU can reach that speed, which is highly likely). Now if you decided that you wanted to aim for 4GHz say then that would require a FSB of 471MHz so with the 1:1 divider the memory would need to run at 942MHz, now if you buy DDR2-800 this is not guaranteed to run at these speeds it might but the is no guarantee, if you bought DDR2-1066 then it would be fine and assuming your CPU would go that fast you could push to 4.53GHz without overclocking the memory.

Hopefully that made some sort of sense...